I'm fixing up an 84 16 and today I noticed this problem on one of the upper gudgeons. The screw in the picture is fine and tightens, the other screw was larger and will not tighten. I removed it and there doesn't appear to be any threads in the hole it came out of. How would this be repaired? I was thinking about maybe going to the one piece version if this would make the repair easier but it looks as if you would use the same holes at the top.

Simply filling the hole and redrilling is not a good idea. The aluminum plate is what the bolt needs to thread into. Filling the hole will do nothing to reconnect the bolt to the aluminum plate as you will just be tapping into putty/resin.

You could go up another bolt size, but you'd be up to a 5/16" bolt since the bolt was already increased once up to a 1/4-20. This means you'd have to remove even more material from the gudgeon. Also, the larger bolt head may interfere with the gudgeon or the rudder casting.

If it were me, I'd install an access port in front of the transom and thru-bolt the gudgeons with 1/4"-20 nuts and bolts.

"Strongest gudgeons available and standard on newer boats! One-piece gudgeons are always in perfect alignment. Excellent replacement for Hobie® 14 or 16 cats that have lost the use of one or more gudgeon screws because this uses 8 fasteners (#19-3520) instead of only 6. Hobie® factory replacement part."

Could I install these leaving out one bolt and get away with not having to put access ports in?

A helicoil may be a workable solution. However, I would not trust threading a gudgeon bolt into thickened epoxy. There is too much load on those bolts and epoxy doesn't have nearly the shear or tensile strength of the aluminum plate. Getting a good bond between epoxy and aluminum can also be difficult if you don't clean the aluminum properly.

You might be able to use the one-piece gugeon if you drilled a new hole just below the existing one and drill and tapped for a new bolt.

But I still think thru-bolting would be the best option. It will be stronger than the original tapped plate. Plus a porthole only costs about $10 as compared to about $40 for the new gugeon. Having access ports also helps with hull ventillation or if you need to do future transom repairs.